The present invention relates to a rocking slag breaker which can effectively break or deform various types of slags generated in iron- and steel-making processes and having a high iron content of 50 to 60% and large sizes ranging between 300 to 500 mm.
Conventionally, most of slags produced in blast furnaces, converters and electric furnaces used in iron- and steel-making processes have been disposed of. In recent years, however, there is an increasing demand for recovery of iron content of the slags and utilization of the slags as aggregates.
The recovery of the iron content is made by magnetically collecting the iron content from the slags in the course of braking of the slags and using the collected iron as the concentrates for making iron and steel. It has been proposed also to grind the slags by means of a rod mill or a self-generating crushing mill. Examples of such known techniques are shown in, for example, Japanese Patent Publication No. 33047/1976 and Japanese Patent Laid-Open Nos. 147416/1976, 151615/1976 and 33163/1977. These known arts are summarized as follows:
(1) The maximum size of the furnace slags treated is up to 300 mm, and does not exceed 500 mm even in special cases.
(2) In most cases, the furnace slags having sizes not greater than 300 mm and having high iron contents of 50 to 60% are used as the concentrates directly or after increase of the iron content up to 90% or higher by a grinding by a rod mill or a self-generating crushing mill.
(3) Furnace slags having small sizes not greater than 300 mm and small iron contents are subjected to crushing, magnetic sorting and sieving to separate slags having comparatively high iron contents. The separated slags are used directly as the concentrates or after a grinding by a rod mill or a self-generating crushing mill for higher iron content.
(4) Furnace slags of sizes greater than 500 mm are subjected to a sorting which is conducted through the aid of a lifting magnet or by visual check and only the slags having small iron content are subjected to breaking into sizes of less than 300 mm. The broken slags are then subjected to various processings.
(5) Furnace slags having sizes exceeding 300 mm and having large iron contents are stacked without any processing and are usually disposed of in the following ways:
(a) crushed by a weight of 2 to 5 tons
(b) cut by means of gas flame
(c) broken by dynamite after drilling
(d) opened with many crossing apertures and broken by means of steel wedge bars.
The work of disposing of the bulky furnace slags greater than 300 mm and having high iron content requires human labour and is quite inefficient. In addition, the workers are subjected to danger due to scattering of small pieces of slags and fragments.
Under these circumstances, there is an increasing demand for furnace slag breaking machines capable of efficiently breaking slags down to sizes of less than 300 mm.
Under this circumstance, the present inventors have experimentally carried out a slag breaking method in which slags greater than 500 mm and rich in iron were broken by application of compressive force. The results of this experiment were as follows:
(1) In the case where the iron is contained as pig iron, such pig iron of iron content up to 100% was broken separated from the slag. The sizes of the slag pieces were concentrated to smaller side of the pig iron size distribution.
(2) In the case where the iron is contained as steel, the slags attaching to or wrapped by the steel were separated as a result of deformation of the steel. Defective parts such as those having internal cavities or blow holes or surface roughness, as well as thin-walled part of the steel, were broken and separated.
(3) As a result of the breaking mentioned in (1) and (2) above, the iron content of the slag was increased without exception to a level of 90% or higher at the greatest.
It has been accepted as a common understanding that metals in furnace slags cannot be broken. Such metals, however, are not homogeneous unlike steel sheets, cast steel and cast iron, but have many surface roughness and cracks, as well as internal defects such as cavities and blow holes. Therefore, when the metals in slags are compressed, stresses are concentrated at the defects so that the metals are easily broken by a comparatively small force.
The inventors have found also that, when the breaking compressive force is applied in the form of three-point bending in which forces of the same direction are applied to both ends of the slag while the central part of the same is subjected to a force acting in the opposite direction, the force required for the breaking is reduced almost to a half of that required for the breaking by a simple compression between two opposing surfaces. With the compression under the application of three-point bending, most of the bulky furnace slags of sizes above 300 to 500 mm could be broken or deformed into sizes below 300 to 500 mm.